Conventionally, drive assisting devices that are mounted in vehicles and assist traveling of the vehicles are known. In order to assist the traveling of a vehicle, such a drive assisting device determines the behavior of the vehicle based on various characteristics of the vehicle. Here, there are various characteristics of the vehicle that vary in accordance with the conditions at the time of traveling. As a device that detects such varying characteristics of a vehicle, for example, there is a device described in Patent Literature 1. In Patent Literature 1, a system that calculates the traveling energy of a vehicle is described. This system determines the traveling energy by calculating grade resistance, air resistance, acceleration resistance, and rolling resistance based on an estimated traveling speed, parameters relating to the vehicle, and parameters relating to a road. In addition, in Patent Literature 2, a device that estimates the weight of a vehicle is described.